In the study of commemorations and translations of feasts there are two words which have a special meaning and which, being often used in calendar working, deserve a special note.  They are “occurrence” and “concurrence.” Occurrence is the conjunction of two or more offices, which fall on the same day.  It may be accidental when two movable feasts are concerned or when a movable feast falls on a day which has a fixed office; or it may be perpetual, when a fixed office falls on a day which already has a fixed office.  The Church does not ask the recitation of a double or a triple office.  She, by her fixed rules, prefers one out of the two of the “occurring” offices, transfers if possible the others, or at least commemorates them by an antiphon, versicle and prayer, and sometimes by a ninth lesson at Matins.

Concurrence is the conjunction of two offices, which succeed one another, so that a question arises as to which feast the Vespers belong to; whether to the feast of the day or to the feast of the following day, or whether the psalms should be of the feast and the remaining part of the Vespers should be as the Ordo so often notes (a cap. de seq.), from the capitulum the office is taken from the following feast.

The new rubrics contain five titles which make certain modifications in the rules hitherto observed.  We thus obtain a ready made division of the subject:—­

(1) Of the precedence of Feasts (Title II.). (2) Of the accidental occurrence of feasts and their translation (Title
    III.).
(3) Of the perpetual occurrence of feasts and their transfer (Title V.). (4) Of the occurrence of feasts (Title V.). (5) Of the commemorations (Title VI.) (Myers and Burton, op. cit.).

The new rubrics without the aid of any commentator give pretty clear notions of the laws of precedence, occurrence and commemoration.  For students in college these rules are expounded in detail with additions, changes, exceptions.  But for priests, long past the student stage, it is difficult to undo the fixed liturgy lore of their student and early priest life; and the need of such a book as The New Psalter and its Uses is, for those interested, a necessity.  Even since the publication of that book, changes have been made.  For example, doubles, major or minor and semi-doubles, which were perpetually excluded on their own day were transferred to some fixed day.  This is given in The New Psalter and its Uses.  But this has now been changed.  In the case of feasts of the universal Church, no translation is allowed now.  But feasts proper to a nation, diocese, order, institute or particular church may still be transferred to a fixed day, if perpetually impeded on their own day.  Another example of necessary changes in that excellent book is in the last paragraph of page 136 (see Decree S.C.R., June, 1912).  The works of compilers and liturgists need constant revision to keep pace with new decisions and decrees.